Protective films or coatings comprising polysaccharides are useful in many different applications, such as protection of all types of surfaces from so called graffiti, traffic pollution, bird droppings, etc.
In EP 0 365 584 B1 there is described a contamination removal process based on the use of a solution containing a polysaccharide and a solvent therefore for creating a protective coating on a surface. After being subjected to contamination, the surface can easily be freed from the contamination by treating the coated surface with a liquid, which is capable of re-dissolving the protective coating.
A number of polysaccharides, for example carrageenans and agar, when dissolved in water at an increased temperature form gels, at certain minimum concentrations when the solution is cooled to a lower temperature. It is known that this property may be used to produce polysaccharide films having an improved stability towards water. If a polysaccharide of the gelling type is used alone, the concentration thereof in solution has to be very low in order to obtain a solution thereof that can be applied to a substrate without difficulty, resulting in thin films. If, on the other hand, the concentration is increased to a level which will result in sufficient film thickness from a single application, then gelling will occur prior to application and the application by spraying or the like will constitute a severe problem.
U.S. Pat. No. 5,948,545 describes a method for protecting a surface from contamination and for facilitating removal thereof using a solution of at least a first polysaccharide and a second polysaccharide, wherein the second polysaccharide or the mixture of the first and second polysaccharide is capable of gel formation. The first polysaccharide is added to the solution to inhibit gel formation in order to allow a higher polysaccharide concentration in the solution while avoiding premature gel formation. A problem associated with the method of U.S. Pat. No. 5,948,545 is that the addition of polysaccharides in order to inhibit gel formation generally results in very high viscosity solutions, which impedes application onto substrates using conventional coating techniques, such as spraying.
Therefore, there is a demand for a new polysaccharide composition which produces protective coatings of sufficient thickness, but without the drawbacks of high viscosity and premature gel formation associated with the prior art methods.